Camptothecin is an alkaloid isolated from Camptotheca acuminata (Wall, et al: J. Am. Chem. Soc., 88, 3888-3890 (1966)), and is known to exhibit antineoplastic activity by inhibiting nucleic acid synthesis (Lown, et al.: Biochem. Pharmacol., 29, 905-915, (1989)). However, as the results of the clinical tests in the United States, the development thereof as a medicine was discontinued because of its toxicity. Thereafter, derivatives of camptothecin are being studied to reduce the toxicity or to increase the activity, yet the problem of the high toxicity has not been solved. For example, irinotecan hydrochloride (Sawada, et al.: Chem. Pharm. Bull., 39, 1446-1454 (1991)), which is the most advanced antineoplastic medicine of camptothecin derivatives, involves problems of side effects of marrow inhibition as well as gastrointestinal toxicity which is considered to be caused by choline esterase inhibition resulting from the carbamoyl structure of the prodrug moiety introduced for making the compound water-soluble (Kawato, et al.: Kiso to Rinsho, 24, 229-234 (1990)).
As another example, 10,11-methylenedioxy-20-O-glycylcamptothecin, which has been reported recently as a water-soluble camptothecin derivative (Wall, et al: J. Med. Chem., 36, 2689 (1993)), has the structure analogous to the compound of the present invention, but has not yet been reported to have antineoplastic activity against solid tumor, and is highly toxic.
Furthermore, most of the camptothecin derivatives are hardly soluble in water, and is not suitable for intravenous administration as general clinical method, which is the great problem in development as a medicine. A fluoroethylcamptothecin derivative was disclosed (JP-A-5-17479) which is derived by changing the ethyl group on 20-position of a camptothecin derivative to a 2-fluoroethyl group having lower toxicity without impairing the antineoplastic activity. Such a compounds is also hardly soluble in water, and development thereof as the injectant is difficult.